It's no secret that we take our sweet ass time developing our products so I've had some OE and aftermarket Nissan VR38DETT engine parts on my desk and in my shop bay for the past couple years. What stood out at first was the stock piston because it doesn't actually stand out at all. It doesn't look like anything that belongs in a high output twin turbo V6. It looks like a scaled up, ultra heavy version of a Nissan xxyyDE (xx=econobox Nissan engine designation, yy=displacement in liters) cast aluminum piston. The only unique features would be the oil cooling chamber underneath the dish of the piston and the hard anodized top ring groove. I'm guessing that Nissan made the VR38DETT piston “strong” by adding plenty of material wherever it was questionable. Adding weight is an effective way to make a piston strong in the case of OEM style fixed operating parameters (480bhp & 7000rpm) and a limited budget ($90k+ for 911 turbo performance). The flip side of course is that when you run the engine outside of those fixed parameters, whatever headroom that Nissan designed into the engine goes away real quick.
I always pay extra attention to pistons because I believe the piston is the most important part of the engine. Sure the sum of the parts is what makes a good engine, but far too many people shrug off how important a piston really is. The piston is usually the most fragile internal component of the bottom end and yet it takes the bulk of the forces created by combustion events. It is has to deal with thermal shock by being constantly massively heated and instantly cooled, accelerated and forced up and down by massive forces, has to transfer these forces to the wristpin and connecting rod all 720° of crank rotation, and all the while it has to be able to live in harmony with smaller components that are inserted into it that are made of unlike steel alloy materials such as wristpins, piston rings, and clips. Keep in mind that the piston also has to slide up and down at a gazillion meters per second against a cylinder bore also made of unlike material. You get the picture: a piston has a lot of things going on compared to the other internal components of an engine. Yet despite all of the critical roles a piston plays within an engine, people continue to take forged pistons for granted.
Way too many people think that just because they have forged pistons, their engine is king fucking kong. In fact, that couldn't be further from the truth. Forged pistons come in a variety of qualities just like exhausts, valves, or any other vehicle components do. A generic shelf piston made to fit your engine might be fine in some cases (e.g. dyno queen, occasional drag racing, to lengthen your forum signature, etc.), but if you plan on really using your engine in real life, you'll need a piston that is specifically designed for your engine that utilizes special materials, special coatings, special machine operations, optimized ring packs, optimized ring heights, optimized compression height and ratio, ultra strong lightweight wristpins, and most importantly a bespoke skirt profile that is designed specifically for your engine (i.e. a NASCAR cup car iron cylinder block skirt profile isn't going to benfit your aluminum, solid deck, sprayed liner VR38). This is where a Cosworth piston comes into the picture. Our shelf pistons come with all of these trick features and are specifically designed for your engine. How and why are we able to perfect pistons for your engine? Because we've been building engines for over 50 years, have some of the world's best engineers at our disposal, and because we actually build and test the engines that we design and manufacture pistons for. We do not have 3000 piston applications in our catalog shared by 10 generic forgings and 12 generic skirt profiles. All Cosworth pistons are machined from bespoke forgings (or in some cases billets). On top of all that, our experience with Nissan's V engines goes far beyond our Performance Parts business.
It really does.
Also extremely important is the quality of the machine work, assembly, and ancilliaries (ECU, injectors, pumps, etc.), and engine tuning. The more attention to detail, the better an engine will perform and the longer it will last. I used to see a lot of engines built with off the shelf generic forged pistons that suffered from “black death” even when owners claimed “I had less than 2000 miles and only had 20 dyno pulls”. At the other extreme, I see Cosworth engines disassembled after 5000 race miles with virtually ZERO scuffing. Premature scuffing can be the fault of ignorant piston manufacturers, lazy machinists, inexperienced engine builders, inexperienced tuners or any combination of.
An example of “black death”
Here's the skirt wear of a Cosworth XFE ChampCar piston after 1500 race miles. The XFE generates 750bhp @ 11,750rpm. The picture doesn't show very clearly where the wear is, but you can see that there's very little skirt wear in total due to correct skirt and ring land profiles.
Here is a piston from a production based, long stroke (94mm) Cosworth YDX Formula Atlantic engine after 2000 race miles. The YDX is based on a Mazda MZR 2.3L and generates 300bhp at 8,500 rpm. No matter what type of engine, Cosworth gets it right.